Ferrites of decreased initial permeability at high frequencies



Oct. 4, 1960 G. H. JONKER EI'AL 2,955,085

FERRITES 0F DECREASEID INITIAL PERMEABILITY AT HIGH mzqusucms Filed Aug. 9, 1956 5 Sheets-Sheet 1 FrcgMc/sec.

FIG. 1

INVENTORS GERARD HEINRICH mm I'IENRICUS PETRUS JOHANNES WIJN PGJL BERNARD BRAUN Oct. 4, 1960 a. H. JONKER ETA'L' 2,955,035

FERRITES OF DECREASED INITIAL PERMEABILITY AT HIGH FREQUENCIES Filed Aug. 9. 1956 l 5 Sheets-Sheet 2 IO 50 I00 5 00 I000 FIG. 2

AGENT 1960 G. H. JONKER ETAL 2,955,035

FERRITES OF DECREASED INITIAL PERMEABILITY AT HIGH FREQUENCIES Filed Aug. 9, 1956 5 She ts-Sheet 3 IO lpo \\-&; 6 060 10 so I00 500 I000 FIG.3

BY M Q AGENT Oct. 4, 1960 G. H. JONKER mm. 7 I 2,955,085

FERRITBS OF DECREASED INITIAL PERMEABILITY AT HIGH FREQUENCIES Filed Aug. 9, 1956 5 Sheets-Sheet 4 IO 0 50 I00 500 I000 Frgg.Mc/sec.

FIG.4

INVENTORS GERARD HEINRICH JONKER HENRICUS PETRUS JOHANNES WIJN POUL BERNARD BRALN AGENT Oct. 4, 1960 s. H. JQNKER ET AL 2,955,035

FERRITES OF DECREASED INITIAL PERMEABILITY AT HIGH FREQUENCIES Filed Aug. 9, 1.956 5 Sheets-Sheet 5 FnqMc/sec.

FIG.5

INVENTORS GERARD HEINRICH JONKER HENRICUS PETRUS JOHANNBVRN AGENT i d s tcsPate O FERRITES OF DECREASED INITIAL PERME- ABILITY AT HIGH FREQUENCIES Gerard Heinrich Jonker, Henricus Petrus Johannes Wijn,

and Poul Bernard Braun, all of Eindhoven, Netherlands, assignors, by mesne assignments, to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Aug. 9,1956, Ser. No. 603,134 Claims priority, application Netherlands Aug. 10, 1955 Claims. (Cl. 252-625) Our invention relates to oxidic ferromagnetic materials,

to methods of preparing these materials and to bodies made from these materials.

Oxidic ferromagnetic materials which exhibit high values of initial permeability are known in the art. AH these materials show a decrease of the initial permeability in a certain frequency range the position of which in the a much higher positioned frequency range than in the.

known materials with an equal low-frequency value of the initial permeability.

Another object of our invention is to provide oxidic ferromagnetic materials which have initial permeabilities of more and often materially more than 2 at frequencies of about 50 mc./s. and often considerably higher frequencies and which exhibit low losses.

Still another object of our invention is to provide oxidic ferromagnetic materials which may serve as materials for magnetic bodies e.g. cores at frequencies of about 50 mc./ s. and often considerably higher frequencies.

These and other objects of our invention will be apparent as the specification progresses.

According to our invention we have found new and novel materials having a composition wherein Q is at least one divalent metal selected from the group consisting of Ba, Sr and Pb, R is at least one divalent metal or complex selected from the group consisting of Mn, Co, Ni, Zn, Mg and Li +Fe 2 T is at least one trivalent metal selected from the group consisting of A1 and Cr,

All these materials have initial permeabilities which do 2,955,085 ,.Pa tented Oct, 4, 1960 not decrease substantially up to very high'frequen'cies. They have initial permeabilities of more and often materially more than 2 at frequencies of about 50 mc./s. and often considerably higher frequencies. Since "they are basically oxidic in nature they are characterized by high ohmic resistances so that eddy current'losses are negligibly small. In addition to having greatly improved initial permeabilities' at high frequencies, particularly above 50 mc./s., the materials of our invention exhibit relatively lowresidual loss factors (tan 6) at frequencies above 50 mc./s.

The novel materials of our invention have a crystal structure which is isomorphic with the material having a unit cell which in the hexagonal crystal system has a c-axis of about 32.8 A. and an a-axis of about 5.9 A., a material known to have permanent magnetic properties but wholly unsuitable as a core material, particularly at frequencies exceeding 50 Inc/s. where its initial permeability is less than 2.

While the entire class of our novel materials have improved magnetic properties, particularly in regard to their initial permeabilities, we have found that materials in which Q is at least one divalent metal selected from-the group consisting of Ba and Sr, R is-at least one divalent metal or complex selected from the group consisting-of Mn, 'Co, 'Ni, Zn, Mgand have moreimproved initialpernre'abilities. V

We have found that materials having even further improved initial permeabilities are' obtained if divalent Co is at least a portion of the metals represented by the term R in the formula representing the chemical composition of our materials described in the last paragraph. We havefurther found that even better results are obtained if the compounds have a composition wherein Q is at least onerdivalent'metal selected from the group consisting of Ba and Sr, -R is at least one divalent metal or complex selected from the group consisting of Mn, Ni, Zn, Mg. and 1 r 111 hi gpgy osysg 1 +y we may use carbonates, oxalates and acetates of the metals. Moreover, instead of metallic oxides we may use one or more preformed reaction products of 'at least two of the metallic oxides.

Preferably we prepare the novel materials of curinvention by heating at a temperature of between 1150 and 1350? C. a finely divided mixture of metallic oxides 'and/ or oxide-forming materials and/or reaction products of metallic oxides, in 'a ratio approximately corresponding to that of the metals in the materials of our invention.

If necessary, the mixture of oxides and/ or equivalent materials may he presintered, usually at a relatively low temperature of about 900 C. to about 1200 C., the

presintered material being reground and resintered sev- (for example BaFelEO and compounds having a spinel structure (for example ooreg or) are formed in addition to the desired compounds, the former compounds not having the desired properties and being convertible only with difliculty into the desired compounds. If presintering is performed, it is not necessary to heat the presintered material rapidly to a temperature of more than 1250" C. during the subsequent sintering operations. j

While we may heat the starting mixtures of these oxides and/or oxide-forming materials to any temperature above 1250 C. we have found that best results are obtained by heating the starting mixtures to a temperature between about 1300" C. and 1370" C. a

In any event the rate of heating should be rapid and preferably the maximum temperature should be reached in 30 minutes.

If the starting mixture contains one or more preformed reaction products of at least two of the metallic oxides,

it is not necessary to heat the starting mixture rapidly to a temperature of more than 1250 C. We then use as a preformed reaction product of at least two of the metallic oxides preferably aniron-containing reaction product, which has been produced at low temperature, preferably below 1100 (3., structure corresponding with that of the mineral magnetoplumbite, for example Ba sr fe O wherein Oxl. J It has been found that, if the sintering operation is carried out in an atmosphere rich in oxygen, compounds of the desired crystal structure are obtained, it is true, but that often the ferrous content is lower. and the ferric content is higher than the values corresponding to the formulae as herein given. Consequently, it appears to be and which has a crystal possible to replace in the formula of our, novel materials part of all of the Fe -ions by Fe -ions. I i case the specific. resistanceis foundto be much higherjhan that of preparations havingythe ferrous content in accordance'with the formulae herein given.

In order to facilitate the sintering operation of our process we may include various flux agents, for example silicates such aspentonite orfluorides such as calcium fluoride in an amount of from 0.25% tof-5%"1n the 'm ixtureoftheoxides. i.

Bodies of desired shape may be formed by sintering the starting mixture directly in the desired shape. Alternatively a product of the desired shape may be formed by regrinding the sintered material of our invention or the presintered material, moulding the resultant powder into the desired shape, and by sintering the moulded product if necessary. A binder such as water, a solution of nitrocellulose or a solution of carboxymethylcellulose may be added to the moulding mixture if necessary.

Ina further embodiment of 'our invention the finely divided material of our invention'is moulded to form a body of the. desired shape by pressing the relative material together with a binding agent which is capable of being hardened, (for example a polyester resinor an ethoxylin resin), followed by. hardening the moulded body. a I

Our invention will now be described in greater detail with reference to the 'followingexamples and drawing. --In the drawing Figs. ltor-5 are graphs showing the relationship between the values of the real portion of initial permeability, i, and the values of the loss factor tan 6 to frequency for various embodiments of our invention. V J

' The relationship between the loss factor tan 6 and the real portion of initial permeability, 7, will be apparent from the following explanation which formsno part of our invention and which is not to be used in any way to limit the scope of our invention: I V

The term ,u' as used hereinmay be explained as follows: A sinusoidally alternating magnetic field with small amplitude will produce a similarly varying inductance in a ferromagnetic body but due to ferromagnetic losses there will be a phase difierence between the magnetic field and the inductance. Thus the permeability of the ferromagnetic body, may be represented by a complex magnitude ,u.=,u.'i,u."'. The real portion of permeability, s, is in phase with the field applied while the other lags in phase by with respect to the applied field. The loss factor tan 6 can then be defined as p I! tan r r i ExA PLBr p A mixture of 20.0 gs. of BaCO 136.0 gs; of Fem,

gs. of ZnO was ground with ethyl alcohol in a porcelain'ball mill for half an hour. Subsequentto drying the oxide mixture and mixing it with a small quantity of a solution or carboxymethylcellulose" as an organic binder, rings were moulded at a pressure of l000 kgs./cm.:-. These rings had an outer diameter 'of about '35 -mms., an inner diameter of about 25 mms. and a height of about 4'mrns. 'Th ese rings were then passed into a furnace at such a rate that within half an hour the hot zone of the furnace which had a temperature of 1320 C. was reached. The rings were kept at this temperature for about one hour and then cooled in the furnace .slowly, i.e. within about three hours, to room temperaturep During this. treatment a flow of air was passed through the furnace. hThefrings: thus fired consisted, as was proved by an X-ray-examinatiom' almost entirely of crystals with the crystal structure isomorphic to that of Breanne,

The properties of these rings arelindicated inthe, table oxide mixture was then heated in air from room temperature to 1300 C. within a period of 20 minutes.

This temperature was maintained for about one hour, after which, this product was cooled to room temperature within a few hours. This reaction product was then reground for about one hour. To this dried ground powder a small supply of a solution of nitrocellulose as an organic binder was added. Then this mixture was moulded at a pressure of 1000 lags/cm? into rings having an outer diameter of about 35 ms, an inner diameter of about 25 mms. and a height of 3 to 4 mms. These rings were heated within a period of one hour from room temperature to 1340 C., then kept at this temperature for one hour and then cooled to room temper-ature within three hours. Throughout the heating period a stream of air was kept flowing through the furnace. X-ray examination showed that the material produced consisted almost entirely of crystals with the crystal structure isomorphic to that of The properties of these rings are indicated in the table under N0. 2 and by the graph of Fig. 1.

EXAMPLE III A mixture of 14.8 gs. of SrCO 136.0 gs. of Fe O and 11.9 gs. of CoCO was ground with ethyl alcohol in a porcelain ball mill for half an hour. Rings were .moulded from the dried product at a pressure of 1000 kgs./cm. and fired in the same manner as described in Example I. X-ray examination proved that the material obtained consisted mainly of crystals with the crystal structure isomorphic to that of and for a small part of crystals with spinel structure. The properties of this material are indicated in the table *under N0. 3 and by the graph of Fig. 2.

EXAMPLE IV EXAMPLE V To the mixture of Example I 3 gs. of LiF was added. Rings were moulded from this mixture at a pressure of 1000 kgs/cm. and fired in the same manner as described in Example I. The properties of these sintered rings are indicated in the table under N0. 5.

In the manner described in Example I many other similar compounds have been produced. The properties of a series of compounds, which are important in the present respects, are indicated in the table under Nos. 6 'to 13.

EXAMPLE VI From BaCO and Fe O in the molecular ratio of 1:56 by heating the mixture for 15 hours at 900 C., a

material was produced, which consisted primarily of the compound BaFe O Of this product was produced, to-

' gether with ZnO, CoCO and Fe O a mixture in a ratio of 1 mol BaFe ors, 0.75 mol C000 0.75 mol ZnO 6 and 2.25 mols Fe O which corresponds to the desired compound ons ons ao iis zv The mixture was ground for four hours with alcohol in avibration mill and then presintered for two hours at 1100 C. in oxygen, after which it was ground for one hour with alcohol in a ball mill. Rings were moulded from the product obtained at a pressure of 1000 kgs./cm. One ring was fired for one hour at 1250 C. in oxygen. The properties of this ring are indicated in the table under No. '14. A further moulded ring was fired for one hour at 1250 C. in air. The properties of this ring are indicated in the table under N0. 15. X-ray examination proved that the material of the two rings consisted primarily of crystals having the structureisomorphic to that of BaFei 'Feigo EXAMPLE vn A mixture of 7.9 gs. of BaCO 3.81 g-s. of OoCO 3.92 gs. of ZnO and 51.2 gs. Fe O was ground with ethyl alcohol in a porcelain ball mill for half an hour. The dried oxide mixture was then heated in 0 from room temperature to 1300 C. within a period of 20 minutes. This temperature was maintained for about one hour, after which this product was cooled to room temperature within a few hours and then ground again with ethyl alcohol in a vibration mill for 4 hours. Rings were moulded from the dried powder at a pressure of 1000 kgs./cm. These rings were heated in 0 at 1300 C. for 1 hour and then cooled in the furnace slowly, i.e. within about-4 hours, to room temperature. During this treatment a flow of 0 was passed through the furnace. The rings thus produced consisted, as was proved by an .X-ray examination, entirely of crystals with the crystal structure isomorphic to that of BaFeE FeE O preparation. In column 2 of the table under the heading of Main Constituent chemical formulae are indicated, which were derived from the composition of the starting mixture and from the fact proved by the X-ray examination that the crystal structure of the compounds concerned is isomorphic to that of the compound values of tan 6 to frequency. In these graphs the values of u? and tan 6 are plotted along the ordinates and the frequencies are plotted along the abscissa.

. While we have described our invention in connection with specific embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

. What we claim is:

V l. A ferromagnetic material consisting essentially of crystals having a composition Q(1x) x ii1y) 2y i r-n isa z-z wherein Q is at least one divalent metal ion selected fiom the group consisting of Ba, Sr and Pb, R is at least one divalent metal ion selected from the group consisting of Mn,.Co, Ni, Zn, Mg and thecomplex Li -J-Fe 2.

T is at least one trivalent metal ion selected from the group consisting of Al and Cr, and wherein at is not greater than /s, y is between A and l, and z is not greater than /5 these crystals having a unit cell which in the hexagonal crystal system has a c-axis of about 32.8 A. and an a-axis of about 5.9 A.

2. A ferromagnetic body having an. initial permeability exceeding 2 at a frequency of at least 50 me./ sec. con- .sisting essentiallyot a highly-coherent mass of crystals .T at least one trivalent metal ion selected from the group consisting of Al and Cr, and wherein x is not greater than 75, y is between A1 and Land 2. is not greater .than fls, these crystals having a unit cell which in the hexagonal crystal system has a c-axis of about 32.8 A. an

ana axisof about 5.9 A;

3. A methodof producing a ferromagnetic material fcompn'sing the stepsjof preparing a finely-divided mixture 3 Table' i Production V 'P' u n '1 N0. Main Constituent r 5 Fig. r Slntering gas glam. .tlem.v 10 50 500 V 1 tango atm. kc./s. Ina/s. mc./s.

1 naznre refi o 1,320 011---. 3.5 3.0 1.5 2 BacoFe Feg O 1,340 air 5.0 5.1 4.7 1 3 sroore reigo 1,320 101...- 4.1 3.1 3.7 3.0 4. BaCo Zn Fe Fe}0 1,320 air 7 7 4 v5 B==.(zn,L1,Fe Fe{o, 1,320 air 42 10 4 3.5 v 1.5 .0 BaCo Zn Je Feg O 1,320 011-.-- 3 0 10 8.5 0.3 0.1 4 BaNiFe Fefifm- 1,320 air r 2.4 2.4 1.7 5 Ba Ou 5ZIl Fg50Feg 7 1,320 O2-.-- 3 7 10 8.5 8.2 4.8 Bao0 Ni Fe Fe 0 1,300 101a... 44 10 5.6 5.5 3.7 naconm regreiioi, 1,320 or.--" 3 2 10 3.2 3.2 2.3 BaznFe Fefi Or o 1,300 o, 2.2 2.1 1.1 BaznFe reEA1o,, 1,300 o 2.0 2.5 1.5 0.5 on ona ms iia 21 1,3 0 0 Y 0.5 0.5 4.2 m m iis it n 1,250 Oz"--- 5.10 0.2 0.3 5.0 BBCoogsz o sF gsF ig w 1,250 Bill-.- 5.10 15.2 11.1 76.6 BaOo Zn Fe 2-; 1,300 0, 7.7 1.0 4.7

greater than /5, y is between V4 and 1, and z is not greater than Vs, these crystals having a unit cell which in the hexagonal crystal system has a c-axis of about 32.8 A. and

ana-axis of about 5.9 A.; and heating said mixture in an atmosphere having at least as much oxygen as t0 a temperature of at least 1100 C. to about 1370 C. to form said crystals, said material having an initial permeability (p1 exceeding 2 at a frequency of at least 5011161360. 5

4. A method of producing a ferromagnetic material comprising the steps; preparing a finely-divided mixture of oxides forming upon heating crystals having a crystal structure corresponding. tothe mineral magnetop'lumbite and consisting of an iron-containing reaction product; heating said mixture to a temperature not greater than 1100 .C. to form said reaction product; preparing a finely-divided mixture of said reaction productand oxides in proportions forming crystals having a composition Qt1fl) x ii1-x ay iiiii-n' mQe-z v wherein Q is at least one'divalent metal ion selected from the group consisting of Ba, Sr and Pb, R is at least one divalent metal ion selected from the group consisting of Mn, Co, Ni, Zn, Mg and the complex Li +Fe 2 T is at least one trivalent metal ion selected from the group consisting of Aland Cr, and wherein x is not greater than' /s, y is between A1. and l, and z is not greater than 5, these crystals having a unit cell which in the hexagonal crystal system has a c-axis of about 32.8 A. and an a-axis of about 5.9 A.; and heating said latter mixture in an atmosphere having at least as much oxygen as air to a temperature of at least 1100 C. to about 1370 C. to form said latter crystals having an initial permeability greater than 2 at frequencies of at least 50 me./ sec.

5. A method of producing a ferromagnetic material comprising the steps, preparing a finely-divided mixture of oxides in proportions forming upon heating crystals of a compound having the composition Qu-a x iii-y) ay iiait-n ml z-l wherein Q is at least one divalent metal ionselected from the group consisting of Ba, Sr and Pb, R is at least one divalent metal ion selected from the group consisting of Mn, Co, Ni, Zn, Mg and the complex Li +Fe 2.

T is at least one trivalent metal ion selected from the group consisting of Al and Cr, and wherein x is not greater than /s, y is between A and 1, and z is not greater than /5, these crystals having a unit cell which in the hexagonal crystal system has a c-axis of about 32.8 A. and an a-axis of about 5.9 A.; heating said mixture to about 900 C. to about 1200 C. to form a reaction product; finely-dividing said reaction product; and heating said finely-divided reaction product in an atmosphere having at least as much oxygen as air to a temperature of at least 1100 C. to about 1370 C. to form said crystals having an initial permeability (n of at least 2 at frequencies of at least 50 mc./ sec.

6. A method of producing a ferromagnetic material comprising the steps, preparing a finely-divided mixture of oxides in proportions forming upon heating crystals having the composition wherein Q is at least one divalent metal ion selected from the group consisting of Ba, Sr and Pb, R is at least one divalent metal ion selected from the group consisting of Mn, Co, Ni, Zn, Mg and the complex Li +Fe 2 T is at least one trivalent metal ion selected from the group consisting of A1 and Cr, and wherein x is not greater than /5 y is between A and l, and z is not greater than /s, these crystals having a unit cell which in the hexagonal crystal system has a c-axis of about 32.8 A. and an a-axis of about 5.9 A.; and heating said mixture in an atmosphere having at least as much oxygen as air to a temperature of 1300 C. to 1370 C. in about 30 minutes to form said crystals having an initial permeability of at least 2 at a frequency of at least 50 mc./sec.

7. A method of producing a ferromagnetic body having an initial permeability exceeding about 2 at frequencies of at least 50 mc./sec. comprising the steps, preparing a finely-divided mixture of oxides in proportions producing upon heating crystals having the composition wherein Q is at least one divalent metal ion selected from the group consisting of Ba, Sr and Pb, R is at least one divalent metal ion selected from the group consisting of Mn, Co, Ni, Zn, Mg and the complex 10 T is at least one trivalent metal ion selected from the group consisting of Al and Cr, and wherein x is not greater than 75, y is between A and 1, and z is not greater than /5, these crystals having a unit cell which in the hexagonal crystal system has a c-axis of about 32.8 A. and an a-axis of about 5.9 A.; compacting said mixture into a body of desired shape and dimensions; and heating said body in an atmosphere having at least as much oxygen as air to a temperature of at least 1100" C. to about 1370 C. to form a highly-coherent body of said crystals.

8. A ferromagnetic material consisting essentially of crystals having a composition:

Q iii-w z iiair-n mm wherein Q is at least one divalent metal ion selected from the group consisting of Ba, Sr, and Pb, R is at least one divalent metal ion selected from the group consisting of Mn, 00, Ni, Zn, Mg, and the complex Li -l-Fe 2 T is a metal selected from the group consisting of Al and Cr, and wherein y is between A and 1, and z is less than Vs, said crystals having a unit cell which in the hexagonal system has a c-axis of about 32.8 A. and an a-axis of about 5.9 A.

9. A ferromagnetic material consisting essentially of crystals having a composition in which p is between /3 and y is not greater than /3, and (p|y) is not greater than 1, and x has a value not greater than 1, said crystals having a unit cell which, in the hexagonal crystal system, has a c-axis of about 32.8 A. and an a-axis of about 5.9 A.

10. A ferromagnetic material consisting essentially of crystals having the composition in which p is between /3 and y is not greater than /3, (p-i-y) is not greater than 1, and x is not greater than 1, said crystals having a unit cell which, in the hexagonal crystal system, has a c-axis of about 32.8 A. and an a-axis of about 5.9 A.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Erchalk et al.: J. Amer. Chem. Soc, Oct. 1946, pp. 2085-2093.

Harvey et al.: RCA Review, Sept. 1, 1950, p. 346. Phillips Technical Review, vol. 13, No. 7, pp. 194-208.

NTgillips Technical Review, vol. 18, pp. -154,

UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No 2,955 O85 October 4 1960 Gerard Heinrich Jonker et a1.

It is hereby certified'that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 63, the composition should read as shown below instead of as in the patent:

Signed and sealed this 18th day of July 1961.,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer 7 v Commissioner of Patents 

1. A FERROMAGNETIC MATERIAL CONSISTING ESSENTIALLY OF CRYSTALS HAVING A COMPOSITION 